1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image in electrophotography, electrostatic recording and electrostatic printing, and to a developer and a process cartridge using the toner.
2. Discussion of the Background
Recent strong demands from the market for higher quality image and energy saving accelerate developing suitable toners and developers therefor. The suitable toner essentially needs to have a small particle diameter and a sharp particle diameter distribution. Individual toner particles having a sharp particle diameter distribution uniformly behave when developing and eminently improve fine dot reproducibility. As a method of preparing such a toner having a sharp particle diameter distribution, polymerization methods such as a suspension polymerization method, an emulsion polymerization method easily deforming toners and a solution suspension method are being used recently.
In order to fix a toner at a lower temperature, a polyester resin having good low-temperature fixability and thermostable preservability is now being used as a binder resin instead of styrene-acrylic resins having conventionally been used. In order to further improve the low-temperature fixability, thermal properties of the resin need controlling. When the resin has too low a glass transition temperature (Tg), the thermostable preservability of the resultant toner deteriorates. When the resin has too low a softening point [T (F½)], hot offset occurrence temperature of the resultant toner lowers. Therefore, even the polyester resin has not yet prepared a toner having good low-temperature fixability and a high hot offset occurrence temperature. Further, since developers in copiers producing images for a long time are stirred for long periods, release agents and polyester resins having a low melting point in toners adhere to carriers, resulting in deterioration of chargeability of the carrier and charge amount of the developer.
Since silica as a fluidizer does not adhere well and moves to concavities of a toner having concavities and convexities, the toner is likely to contaminate a photoreceptor and adhere to a fixing roller. Although having a merit of using a low-temperature fixable polyester resin, the solution suspension method adds a polymeric material in a solution or a dispersion of a resin and a colorant to improve releasability of the resultant toner so as to be an oilless fixable toner. Therefore, the solution or the dispersion has high viscosity and likely to lower the productivity. Japanese published unexamined application No. 9-15903 discloses a method of preparing a toner a developing an electrostatic latent image, including a process of mixing a binder resin and a colorant in a solvent which is not miscible with water to prepare a composition, a process of dispersing the composition in an aqueous medium under the presence of a dispersion stabilizer to prepare a suspension, a process of removing the solvent from the suspension upon application of heat and/or depressure to form particles having concave and convex surfaces and a process of spheronizing or deforming the particles. However, the resultant irregular-formed toner us unstably charged and is not designed to be polymeric to have basic durability and releasability.
Because of these reasons, a need exists for a toner having a small particle diameter and a sharp particle diameter distribution to produce high-definition images having good fine dot reproducibility, good hot offset resistance, low-temperature fixability, and no deterioration of chargeability adhering less to a carrier even when used for long periods.